The invention concerns a method of checking the plausibility of measured values. More precisely, the invention concerns a method of checking the plausibility of measured values of the same measured variable, said values being generated by unsynchronised sensors in a motor vehicle environment.
For capturing and processing measured values in safety-relevant systems, sub-tasks are usually achieved with redundancy, to keep the probability of faults and failures of the whole system low. This can include the capture of one and the same measured variable by multiple sensors of the same or different kinds. It is usually assumed that the probability of a defect of a single component is many times greater than a defect of two components which are provided in parallel at the same instant.
For instance, the speed of rotation of a motor vehicle around its vertical axis, the so-called yaw rate, can be captured by two sensors and passed on to a processing unit, which itself is part of a system for automatic steering interventions to stabilise the vehicle. The intervention times of such a steering system are very short, since a wrongly generated steering moment can have a safety-critical effect within a few milliseconds (typically 50-100 ms). In the processing unit, therefore, the malfunction of one of the sensors must be quickly and reliably detected, to be able to switch the automatic steering system off in good time and warn the driver.
It must be taken into account that the measurement times of the sensors are not necessarily synchronised, and therefore comparing the values is not immediately possible. If the measured values are transmitted via a bus with priority arbitration as is usual today, it is also not guaranteed that the measured values reach the processing unit in the sequence in which they were captured.
In the prior art, devices which use the change of measured values over time for fault detection are known. Such a device is described in patent application DE 199 23 688 A1, and corresponding U.S. Pat. No. 6,507,198B1, both of which are incorporated by reference herein. A fault state is assumed if the signal changes of the sensors do not correlate with each other. The described device is not designed to process measured values which refer to different measurement times.
Patent application DE 195 25 217 A1 concerns a method of evaluating safety-critical measured variables using two independent measurement channels, of which one measurement channel captures the whole measurement range, and the other captures only a partial measurement range. However, the described method is also not designed to process measured values which refer to different measurement times.
The invention is therefore based on the object of determining the plausibility of unsynchronised measured values of at least two sensors of the same measured variable in the motor vehicle environment.